使用Hibernate加入JOIN的問題

Question

我是JAVA中Hibernate的初學者，不知道如何解決這個問題

我有兩張桌子：Usuario和Certificado，我想創建一個關系和他們的關系。

Class Certificado：

@Entity
@Table(name = "Certificado",
       uniqueConstraints = { @UniqueConstraint( columnNames = { "identifierUnique", "handleUser" } ) } )
public class Certificado {
    @Id
    @GenericGenerator(name="generator", strategy="increment")
    @GeneratedValue(generator="generator")
    private int handle;
    @Column(length = 255)
    @Column
    private int handleUser;

    @ManyToOne
    @JoinColumn(name="handle_user", referencedColumnName="handle")
    private Usuario usuario;
}

Usuario類：

@Entity
@Table(name = "Usuario")
public class Usuario {
    @Id
    @GenericGenerator(name="generator", strategy="increment")
    @GeneratedValue(generator="generator")
    private int handle;
    @Column(length = 255, unique = true)
    private String email;   
    @Column(length = 20)
    private String password;    
    @OneToMany(mappedBy="usuario", cascade = CascadeType.ALL, fetch = FetchType.LAZY)
    private Set<Certificado> certificados;

        ...
}

當我執行SQL函數時：

public static List<Object[]> loadCertificado30DaysBeforeExperation() throws Exception{      
        Session.begin();
        try {
            try {
                String select = "SELECT c FROM Certificado c "
                    + "LEFT JOIN c.handleUser AS user";
                return Session.list(select);
            } catch (Exception e) {
                throw e;
            }
        } finally {
            Session.commit();
        }
    }

錯誤：

   java.lang.NullPointerException

堆棧跟蹤：

java.lang.NullPointerException
    at org.hibernate.hql.internal.ast.HqlSqlWalker.createFromJoinElement(HqlSqlWalker.java:393)
    at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.joinElement(HqlSqlBaseWalker.java:3645)
    at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.fromElement(HqlSqlBaseWalker.java:3431)
    at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.fromElementList(HqlSqlBaseWalker.java:3309)
    at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.fromClause(HqlSqlBaseWalker.java:706)
    at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.query(HqlSqlBaseWalker.java:562)
    at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.selectStatement(HqlSqlBaseWalker.java:299)
    at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.statement(HqlSqlBaseWalker.java:247)
    at org.hibernate.hql.internal.ast.QueryTranslatorImpl.analyze(QueryTranslatorImpl.java:249)
    at org.hibernate.hql.internal.ast.QueryTranslatorImpl.doCompile(QueryTranslatorImpl.java:184)
    at org.hibernate.hql.internal.ast.QueryTranslatorImpl.compile(QueryTranslatorImpl.java:137)
    at org.hibernate.engine.query.spi.HQLQueryPlan.<init>(HQLQueryPlan.java:105)
    at org.hibernate.engine.query.spi.HQLQueryPlan.<init>(HQLQueryPlan.java:80)
    at org.hibernate.engine.query.spi.QueryPlanCache.getHQLQueryPlan(QueryPlanCache.java:168)
    at org.hibernate.internal.AbstractSessionImpl.getHQLQueryPlan(AbstractSessionImpl.java:221)
    at org.hibernate.internal.AbstractSessionImpl.createQuery(AbstractSessionImpl.java:199)
    at org.hibernate.internal.SessionImpl.createQuery(SessionImpl.java:1778)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at org.hibernate.context.internal.ThreadLocalSessionContext$TransactionProtectionWrapper.invoke(ThreadLocalSessionContext.java:352)
    at com.sun.proxy.$Proxy15.createQuery(Unknown Source)
    at br.com.persistence.Session.list(Session.java:96)
    at br.com.utils.ServletUtils.loadCertificado30DaysBeforeExperation(ServletUtils.java:134)
    at br.com.monitoramento.MonitorThread.run(MonitorThread.java:25)

Answer 1

Hibernate的HQL不支持間隔（ 並且通常具有極差的日期數學支持 ）。

您需要使用本機SQL，或通過在Java端本地執行日期計算來無interval表達查詢。

或者您可以注冊用戶定義的SQL函數並創建一個PostgreSQL函數來執行您想要的日期數學運算。

看到：

• 在HQL中執行日期/時間數學？
• 如何在hibernate標准中使用date（）
• Hibernate Criteria：NOW（）<date + 1 day
• HQL中的日期操作

還有很多。

Answer 2

您是否嘗試過30天內從'30' - >間隔刪除''。 或者逃避'30' - > \\ '30 \\'。